Optimized layer-2 network switching systems and methods

ABSTRACT

An exemplary method includes monitoring a performance of at least one of a plurality of layer-2 network paths connecting a layer-2 network switch device to another layer-2 network switch device and selecting an optimal one of the plurality of layer-2 network paths over which to forward data traffic based on a path selection heuristic and the monitored performance of the at least one of the plurality of layer-2 network paths. At least a portion of the exemplary method may be performed by a layer-2 network switching system. In certain embodiments, the selecting of the optimal one of the plurality of layer-2 network paths over which to forward the data traffic is based on at least one of a latency parameter, a congestion parameter, and a cost parameter associated with the at least one of the plurality of layer-2 network paths. Corresponding systems and methods are also disclosed.

BACKGROUND INFORMATION

Communication networks provide many people and organizations with accessto a variety of applications and services. A typical communicationnetwork employs a layered communication and protocol design in whicheach layer represents a collection of conceptually similar functions.The layers are arranged hierarchically, with each layer typicallyproviding services to the layer above it and requesting services fromthe layer below it.

As an example, a typical layered design of a communication networkpatterned after the Open Systems Interconnection (“OSI”) reference modelincludes a physical layer, data link layer, network layer, transportlayer, session layer, presentation layer, and application layer arrangedhierarchically. The physical layer, data link layer, and network layerare commonly referred to as “media layers,” and the other four layersare commonly referred to as “host layers.”

The physical layer includes functions concerned with interactionsbetween network devices and a physical medium. The data link layerincludes functions concerned with transfer of data traffic acrossphysical links interconnecting network entities. The network layerincludes functions for end-to-end routing (e.g., source to destination)of data traffic. Typically, the data link layer receives and responds toservice requests from the network layer by issuing service requests tothe physical layer for transport of data frames across physical links.

Conventionally, the data link layer is not concerned with pathdetection, data traffic routing, error control, quality-of-service, andother “intelligence-type” functions that are left to the network layer.To illustrate, a data link layer switch device such as a conventionalEthernet switch device typically receives a service request from thenetwork layer and simply forwards data traffic frames associated withthe request to a port that has been mapped to a destination address,such as a Media Access Control (“MAC”) address, indicated in the servicerequest. The port provides a connection to a physical link connectingthe Ethernet switch device to another Ethernet switch device associatedwith the MAC address.

While the simple data traffic forwarding functionality of a data linklayer device such as a conventional Ethernet switch device iswell-suited for certain types of communication networks such as asmall-scale local area network, it is problematic for other types ofcommunication networks. For example, traditional Ethernet switch devicesand protocols tend to cause congestion in optical transport networks andparticularly in hybrid data link layer and optical transport networkconfigurations. The congestion may be especially problematic when suchhybrid configurations are used to transport significant loads of datatraffic over large-capacity physical links and/or large geographic areassuch as may be used in a backhaul network and/or a wide area network(e.g., a metro area network). To illustrate, a traditional Ethernetswitch device is designed to maximize throughput over a physical linkconnecting two network devices. Accordingly, the Ethernet switch devicewill blindly forward data traffic frames over the physical link withoutconsidering the congestion, cost, or latencies associated with the link.

While the network layer is typically configured to perform pathdetection, data traffic routing, error control, quality-of-service(“QOS”), and other “intelligence-type” functions, such functions at thenetwork layer do not always prevent congestion of physical linksinterconnecting network devices. Moreover, overhead associated with thenetwork layer is significantly more than overhead associated with thedata link layer. Thus, there is a need to optimize data trafficforwarding at the data link layer in communication networks such asoptical transport networks.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings illustrate various embodiments and are a partof the specification. The illustrated embodiments are merely examplesand do not limit the scope of the disclosure. Throughout the drawings,identical or similar reference numbers designate identical or similarelements.

FIG. 1 illustrates an exemplary layer-2 network switching system.

FIG. 2 illustrates an exemplary layer-2 network switch device with thesystem of FIG. 1 implemented thereon.

FIG. 3 illustrates an exemplary network system having a plurality ofnetwork switch devices interconnected by a plurality of links.

FIG. 4 illustrates an exemplary layer-2 network switching method.

FIG. 5 illustrates an exemplary layer-2 network path performancemonitoring method.

FIG. 6 illustrates an exemplary path comparison table.

FIG. 7 illustrates an exemplary layer-2 network path performancemonitoring method.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Exemplary optimized layer-2 network switching systems and methods aredescribed herein. As described herein, exemplary systems and methods maymonitor a performance of at least one of a plurality of layer-2 networkpaths and select an optimal one of the plurality of layer-2 networkpaths over which to forward layer-2 data traffic based on a pathselection heuristic and the monitored performance of the at least one ofthe plurality of layer-2 network paths. Data traffic may then beforwarded over the selected optimal layer-2 network path.

For example, an exemplary method includes monitoring a performance of atleast one of a plurality of layer-2 network paths connecting a layer-2network switch device to another layer-2 network switch device andselecting an optimal one of the plurality of layer-2 network paths overwhich to forward data traffic based on a path selection heuristic andthe monitored performance of the at least one of the plurality oflayer-2 network paths. At least a portion of the exemplary method may beperformed by a layer-2 network switching system. In certain embodiments,the selecting of the optimal one of the plurality of layer-2 networkpaths over which to forward the data traffic is based on at least one ofa latency parameter, a congestion parameter, and a cost parameterassociated with the at least one of the plurality of layer-2 networkpaths. Corresponding systems and methods are also disclosed.

As used herein, the term “layer-2” refers to a particular layer of alayered network communication and protocol design. More specifically,the term “layer-2” may refer to a layer that interfaces with andrequests services from a physical layer (“layer-1”) that is responsiblefor interfacing directly with a physical transport medium (e.g., anoptical transport medium such as optical fiber). In the Open SystemsInterconnection (“OSI”) reference model, for example, the term “layer-2”refers to the data link layer, which is configured to interface with andrequest services from the physical layer of the OSI reference model. Incertain embodiments, layer-2 may refer specifically to an Ethernet layerand/or a Media Access Control (“MAC”) addressing layer of a layerednetwork communication and protocol design.

The physical transport medium with which elements of layer-1 interfacemay include any medium suitable for transporting data traffic. Incertain embodiments, for example, the physical transport mediumcomprises an optical transport medium (e.g., optical fiber) such as maybe employed in an optical transport network.

Layer-2 elements may be separate from or integrated with layer-1elements. For example, layer-2 devices may be separate from layer-1devices, or layer-2 and layer-2 elements may be integrated in a singledevice. In certain embodiments, layer-2 and layer-1 elements may beintegrated to form a hybrid layer-2 optical transport network.

Exemplary embodiments of optimized layer-2 network switching systems andmethods will now be described in more detail with reference to theaccompanying drawings.

FIG. 1 illustrates an exemplary layer-2 network switching system 100 (orsimply “system 100”). As will be described in more detail below, system100 may be configured to monitor a performance of one or more layer-2network paths and select an optimal one of the layer-2 network pathsover which to forward data traffic based on a path selection heuristicand the monitored performance of the one or more layer-2 network paths.

System 100 may include, but is not limited to, a user interface facility102, a communication facility 104, a forwarding facility 106, amonitoring facility 108, and a data storage facility 110 communicativelycoupled one to another. Facilities 102-110 may be configured to performone or more operations related to layer-2 functionality of elements ofcommunications network, as described herein.

User interface facility 102 may be configured to provide a userinterface through which a user of system 100 may provide input andreceive output related to layer-2 functionality. Accordingly, a user ofsystem 100 may input data, settings, and/or parameters to system 100 andreceive output such as performance reports related to layer-2functionality through user interface facility 102. User interfacefacility 102 may employ any technologies suitable for providing a userinterface.

Communication facility 104 may be configured to transmit and receivecommunications and/or data related to layer-2 functionality. Forexample, communication facility 104 may send and receive inter-layercommunications. Accordingly, communication facility 104 may receive andrespond to service requests from a layer (e.g., a network layer(“layer-3”) hierarchically above layer-2) and provide service requeststo another layer (e.g., a physical layer (“layer-1”) hierarchicallybelow layer-2).

In addition, communication facility 104 may transmit and receiveintra-layer communications and/or data to/from one or more layer-2network devices over one or more layer-2 network paths and/or linksinterconnecting layer-2 network devices. Communication facility 104 mayinclude any technologies suitable for transmitting and receiving layer-2communications and/or data. In certain embodiments, communicationfacility 104 may be configured to interface with one or more ports of anetwork device, which ports may comprise ingress and/or egress portsto/from layer-2 network paths and/or links interconnecting networkdevices.

Forwarding facility 106 may be configured to forward layer-2 datatraffic for transport over one or more layer-2 network paths and/orlinks. For example, forwarding facility 106 may forward data traffic toan ingress port mapped to a layer-2 network path and/or link fortransport over the layer-2 network path and/or link.

In certain embodiments, forwarding facility 106 may be configured toforward data traffic based on forwarding data 112 stored in data storagefacility 110. Forwarding data 112 may include any data that may be usedby forwarding facility 106 to determine a forwarding destination (e.g.,a forwarding address and/or port). For example, forwarding data 112 mayinclude a traffic forwarding table including data representative ofnetwork device addresses (e.g., MAC addresses associated with networkinterface cards) and ports associated with the network device addresses.Accordingly, forwarding facility 106 may locate a destination networkdevice address in the forwarding table and identify a port to which datatraffic addressed to the destination network device address is to beforwarded. As described further below, in certain embodiments, a trafficforwarding table may be maintained and updated based on monitoredperformance of one or more layer-2 network paths.

Monitoring facility 108 may be configured to monitor a performance of atleast one of a plurality of layer-2 network paths and select an optimalone of the plurality of layer-2 network paths over which to forwardlayer-2 data traffic based on a path selection heuristic and themonitored performance of the at least one of the plurality of layer-2network paths. In certain examples, the selection of the optimal pathmay be based on path data 114 and path selection heuristic data 116stored in data storage facility 110. Path data 114 may include any datarelated to one or more layer-2 network paths, including datarepresentative of the monitored performance of one or more layer-2network paths. In certain embodiments, path data 114 may include a pathcomparison table including data representative of path performancemetrics. As described further below, a path comparison table may bemaintained and updated based on monitored performance of one or morelayer-2 network paths. Path selection heuristic data 116 may include anydata representative of a path selection heuristic that may be used toselect an optimal layer-2 network path over which to forward datatraffic. The path selection heuristic may be defined such that aselection of an optimal layer-2 network path is based on monitoredperformance parameters of one or more layer-network paths. Examples ofmonitoring the performance of one or more layer-2 network paths andselecting an optimal one of the paths over which to forward layer-2 datatraffic based on a path selection heuristic and the monitoredperformance of the one or more paths are described in detail furtherbelow.

Storage facility 110 may be configured to maintain forwarding data 112,path data 114, and path selection heuristic data 116. Storage facility110 may be further configured to maintain any other data as may serve aparticular application.

System 100, including facilities 102-110, may include any computerhardware and/or computer-implemented instructions (e.g., software), orcombinations of computer-implemented instructions and hardware,configured to perform one or more of the processes described herein. Inparticular, system 100 may be implemented on one physical computingdevice or may be implemented on more than one physical computing device.Accordingly, system 100 may include any number of computing devices, andmay employ any of a number of computer operating systems. Moreover, itwill be recognized that although facilities 102-110 are shown to beseparate facilities in FIG. 1, any of those facilities may be combinedinto a single facility as may serve a particular application.

Accordingly, one or more of the processes described herein may beimplemented at least in part as instructions executable by one or morecomputing devices. In general, a processor (e.g., a microprocessor)receives instructions, from a computer-readable medium, (e.g., a memory,etc.), and executes those instructions, thereby performing one or moreprocesses, including one or more of the processes described herein. Suchinstructions may be stored and/or transmitted using any of a variety ofknown computer-readable media.

A computer-readable medium (also referred to as a processor-readablemedium) includes any medium that participates in providing data (e.g.,instructions) that may be read by a computer (e.g., by a processor of acomputer). Such a medium may take many forms, including, but not limitedto, non-volatile media and/or volatile media. Non-volatile media mayinclude, for example, optical or magnetic disks and other persistentmemory. Volatile media may include, for example, dynamic random accessmemory (“DRAM”), which typically constitutes a main memory. Common formsof computer-readable media include, for example, a floppy disk, flexibledisk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM,DVD, any other optical medium, a RAM, a PROM, an EPROM, a FLASH-EEPROM,any other memory chip or cartridge, or any other medium from which acomputer can read.

FIG. 2 illustrates components of an exemplary layer-2 network switchdevice 200 (or simply “device 200”), which may have system 100implemented thereon. As shown in FIG. 2, device 200 may include acommunication interface 202, a processor 204, a storage device 206, aninput/output (“I/O”) module 208, a forwarding module 210, and amonitoring module 212 communicatively coupled one to another by way of acommunication infrastructure 214. The components of device 200 maycommunicate with one another, including sending data to and receivingdata from one another, using any suitable communication technologies.Moreover, the components of device 200 may be implemented on any layer-2network device, such as an Ethernet switch device, a MAC address switchdevice, a multi-layer switch device, an optical transport networkinterface device, and any other layer-2 device configured to perform oneor more of the processes and/or operations described herein.

In some examples, user interface facility 102, communication facility104, forwarding facility 106, monitoring facility 108, and/or storagefacility 110 of system 100 may be implemented by or within one or morecomponents of device 200. For example, computer-readable instructions(e.g., applications 216) residing within storage device 206 may beconfigured to direct processor 204 to perform one or more processes orfunctions associated with user interface facility 102, communicationfacility 104, forwarding facility 106, and/or monitoring facility 108.Likewise, storage facility 108 may be implemented by or within storagedevice 206.

While an exemplary device 200 is shown in FIG. 2, the componentsillustrated in FIG. 2 are not intended to be limiting. Additional oralternative components may be used in other embodiments. Components ofthe device 200 shown in FIG. 2 will now be described in additionaldetail.

Communication interface 202 may be configured to perform one or more ofthe functions of communication facility 104, including transmittingand/or receiving communications and/or data to/from non-layer-2 layersof a layered network communication and protocol design and/or to/fromone or more other layer-2 network devices. Examples of communicationinterface 202 may include, without limitation, one or more layerinterfaces, application program interfaces, interfaces (e.g., ports) toone or more layer-2 network paths and/or links, transceivers,transmitters, receivers, and any other suitable interface.

Processor 204 generally represents any type or form of processing unitcapable of processing data or interpreting, executing, and/or directingexecution of one or more of the instructions, processes, and/oroperations described herein. Processor 204 may direct execution ofoperations in accordance with computer-executable instructions such asmay be stored in storage device 206 or another computer-readable medium.

Storage device 206 may include one or more data storage media, devices,or configurations and may employ any type, form, and combination of datastorage media and/or device. For example, storage device 206 mayinclude, but is not limited to, a hard drive, network drive, flashdrive, magnetic disc, optical disc, random access memory (“RAM”),dynamic RAM (“DRAM”), other non-volatile and/or volatile data storageunits, or a combination or sub-combination thereof. Electronic data,including data described herein, may be temporarily and/or permanentlystored in storage device 206.

I/O module 208 may be configured to perform one or more of the functionsof user interface facility 102, including receiving input from andproviding output to a user. In certain embodiments, I/O module 208 isconfigured to receive user input in the form of data, settings, and/orparameters related to layer-2 functionality. I/O module 208 may includeany hardware, firmware, software, or combination thereof supportive ofinput and output capabilities.

Forwarding module 210 may be configured to perform one or more of thefunctions of forwarding facility 106, including forwarding layer-2 datatraffic as described above.

Monitoring module 212 may be configured to perform one or more of thefunctions of monitoring facility 106, including monitoring performanceof at least one of a plurality of layer-2 network paths connected todevice 200 and selecting one of the plurality of layer-2 network pathsover which to forward data traffic based on a path selection heuristicand the monitored performance. As described further below, in certainembodiments, monitoring module 212 and/or monitoring facility 108 may beconfigured to monitor path performance and/or select an optimalforwarding path based on monitored path performance in one or morebackground processes running on device 200.

Monitoring module 212 may include any hardware, computer-readableinstructions, or combination thereof configured to perform one or moreof the monitoring and/or selecting operations described herein. Incertain embodiments, monitoring module 212 may implemented ascomputer-readable instructions stored in storage device 206 andconfigured to direct processor 204 and/or one or more other componentsof device 200 to perform one or more of the monitoring and/or selectingoperations described herein.

FIG. 3 illustrates an exemplary network system 300 (or simply “system300”) having a plurality of network switch devices interconnected by aplurality of links. One or more components of system 100 and/or device200 may be implemented by, within, and/or across one or more of thenetwork switch devices in system 300.

As shown in FIG. 3, system 300 may include a plurality of layer-2network switch devices 302 (e.g., layer-2 network switch devices 302-1through 302-5) interconnected by a plurality of links 304 (e.g., links304-1 through 304-6). Layer-2 network switch devices 302 (or simply“devices 302”) may comprise any layer-2 network devices, such as devices200, Ethernet switch devices, MAC address switch devices, multi-layerswitch devices, optical transport network interface devices, any otherlayer-2 devices configured to perform one or more of the layer-2processes and/or operations described herein, or any combination orsub-combination of such devices.

In certain embodiments, devices 302 may be located at geographicallyremote sites interconnected by links 304 as shown in FIG. 3. Forexample, devices 302 may be located at various cell sites, repeaterstations, and/or switching offices within a mobile phone network. Asanother example, devices 302 may be located at remote geographiclocations and may form at least part of a wide area network (e.g., ametro area network), a backhaul network, a core transport network, orother network having geographically remote locations.

Links 304 may comprise physical links over which data traffic may betransported between devices 302. Links 304 may include or be formed byany suitable physical transport media interconnecting devices 302. Incertain embodiments, links 304 may include or be formed over opticaltransport media such as optical fibers, Synchronous Optical Networking(“SONET”) protocol connections, and/or Synchronous Digital Hierarchy(“SDH”) connections interconnecting devices 302. As an example, links304 may include or be formed over OC-48 and/or 10-Gigabit Ethernetconnections. In certain examples, links 304 may comprise virtualconcatenation groups (“VCGs”), which may include groupings of opticalconnections interconnecting certain devices 302.

Layer-2 network paths may be provisioned over one or more links 304between devices 302 to form end-to-end layer-2 data transportconnections between devices 302. As shown in FIG. 3, system 300 mayinclude one or more provisioned layer-2 network paths 306 (e.g., layer-2network paths 306-1 through 306-3) interconnecting one or more devices302. The layer-2 network paths 306 (or simply “paths 306”), which arerepresented by dashed lines in FIG. 3, may provide end-to-end paths overwhich layer-2 data traffic may be transported between devices 302. InFIG. 3, layer-2 network paths 306-1, 306-2, and 306-3 provide aplurality of end-to-end paths between devices 302-1 and device 302-3.Specifically, path 306-1 spans link 304-1, device 302-2, and link 304-2to provide an end-to-end path between device 302-1 and device 302-3,path 306-2 spans link 304-5, device 302-5, link 304-4, device 302-4, andlink 304-3 to provide another end-to-end path between device 302-1 anddevice 302-3, and path 306-3 spans link 304-5, device 302-5, and link304-6 to provide yet another end-to-end path between device 302-1 anddevice 302-3.

Paths 306 may be provisioned in any suitable way in system 300. Incertain embodiments, one or more paths 306 may be manually provisionedbetween devices 302 using available links 304. In other embodiments, oneor more paths 306 may be automatically discovered and provisioned usingany suitable path discovery protocol. In certain examples, paths 306 maybe provisioned as virtual local area networks (“VLANs”) interconnectingdevices 302. A VLAN may span one or more links 304, and a link 304 maysupport one or more VLANs.

In certain embodiments, system 100 may include or be implemented withinan optical transport network and/or a hybrid layer-2 optical transportnetwork. In such embodiments, links 304 may include and/or be formedover optical transport media. In some examples, devices 302 may compriseEthernet switch devices and/or MAC addressing devices configured toforward layer-2 data traffic over links 304 and/or paths 306 asdescribed above.

Examples of monitoring a performance of at least one of a plurality oflayer-2 network paths and selecting an optimal one of the plurality ofpaths over which to forward data traffic based on a path selectionheuristic and the monitored performance of at least one of the pathswill now be described. In some of the examples described below,reference will be made to system 300 in which device 302-1 may monitor aperformance of at least one of the paths 306 shown in FIG. 3 andselecting an optimal one of the paths 306 over which to forward datatraffic to device 302-3 based on a path selection heuristic and themonitored performance of the path(s). Such examples are illustrativeonly and not limiting in any sense.

FIG. 4 illustrates an exemplary optimized layer-2 network switchingmethod 400. While FIG. 4 illustrates exemplary steps according to oneembodiment, other embodiments may omit, add to, reorder, and/or modifyany of the steps shown in FIG. 4. In certain embodiments, system 100,device 200, and/or one or more devices 302 may perform one or more ofthe steps shown in FIG. 4.

In step 402, a performance of at least one of a plurality of layer-2network paths is monitored. For example, a performance of at least oneof the paths 306 interconnecting device 302-1 and device 302-3 in FIG. 3may be monitored.

A performance of at least one of a plurality of layer-2 network pathsmay be monitored in any suitable way in step 402. For example, FIG. 5illustrates an exemplary layer-2 network path performance monitoringmethod 500. While FIG. 5 illustrates exemplary steps according to oneembodiment, other embodiments may omit, add to, reorder, and/or modifyany of the steps shown in FIG. 5. In certain embodiments, system 100,device 200, and/or one or more devices 302 may perform one or more ofthe steps shown in FIG. 5.

In step 502, a ping message is transmitted over at least one of theplurality of layer-2 network paths. For example, a ping message may betransmitted from device 302-1 to device 302-3 over at least one of thepaths 306 shown in FIG. 3. Device 302-3 may receive the ping message andtransmit a response to the ping message over at least one of the paths306. In some examples, a response to the ping message may be transmittedfrom device 302-3 to device 302-1 over each of the paths 306 used totransport the ping message from device 302-1 to device 302-3.

In step 504, a response to the ping message is received over at leastone of the plurality of layer-2 network paths. For example, device 302-1may receive a response to the ping message from device 302-3 over atleast one of the paths 306. In some examples, device 302-1 may receive aresponse to the ping message over each of the paths 306 used to transmitthe ping message from device 302-1 to device 302-3.

In step 506, a performance of at least one of the plurality of layer-2network paths is determined based on the response received in step 504.For example, a performance of at least one of the paths 306interconnecting device 302-1 and device 302-3 may be determined based onthe response received in step 504. In some examples, a performance ofeach of the paths 306 used to transport a ping message and a response tothe ping message may be determined based on the response received instep 504.

The determined performance of at least one of the plurality of layer-2network paths may include one or more performance parameters indicativeof the performance of one or more of the layer-2 network paths intransporting the ping message and/or the response to the ping messagebetween layer-2 network devices. In certain embodiments, for example,step 506 may include determining a latency parameter and/or a congestionparameter for at least one of a plurality of layer-2 network paths. Thelatency parameter, which may include a queuing, transport, and/or otherlatency parameter, may be determined in any suitable way, such as byusing timestamps included in the response to the ping message tocalculate the latency parameter. The congestion parameter may also bedetermined in any suitable way. In certain embodiments, for example, theping message may comprise a chain of data packets spaced apart by atransmission time interval. The response to the ping message may includetimestamps associated with reception of the ping message. The receipttimestamps may be used to detect any deviation in a receipt timeinterval from the transmission time interval. Such a detected deviationfrom a transmission time interval may be used to calculate a latencyparameter and/or a congestion parameter for a layer-2 network path.

As an example, device 302-1 may transmit a ping message including achain of data packets to device 302-3 over at least one of the paths306. Each sequential pair of the data packets may be spaced apart by atransmission time interval. Device 302-3 may receive the chain of datapackets and record timestamps representative of times at which each ofthe data packets is received. Device 302-3 may insert the timestampinformation in a response to the ping message and send the response todevice 302-1 over at least one of the paths 306. The timestamp dataincluded in the response to the ping message may be accessed and used todetermine a latency parameter and/or a congestion parameter for one ormore of the paths 306. For example, a latency parameter (e.g., a queuinglatency parameter) and/or a congestion parameter may be determined bydetecting a deviation from a transmission time interval at which a chainof data packets is spaced apart at transmission and calculating thelatency parameter and/or the congestion parameter based at least in parton the detected deviation from the transmission time interval.

One or more performance parameters, such as a latency parameter and acongestion parameter may be determined in step 506 for either directionor for both directions of transport over at least one of the layer-2network paths. For example, data associated with transport of a pingmessage from device 302-1 to device 302-3 may be used to determine adirectional performance of a path 306 in a direction from device 302-1to device 302-3, and transport of a response to the ping message fromdevice 302-3 to device 302-1 may be used to determine a directionalperformance of the same path 306 in the opposite direction (from device302-3 to device 302-1). Accordingly, in certain examples, bidirectionalpath performance parameters may be determined in step 506.

Determination of a latency parameter and/or a congestion parameter instep 506 is illustrative only. Additional and/or alternative performanceparameters may be determined in other embodiments.

In step 508, a path comparison table may be maintained and updated withdata representative of the performance determined in step 506. Forexample, monitoring facility 108 of system 100 may maintain datarepresentative of a path comparison table in path data 114 of datastorage facility 110, as mentioned above. The path comparison table maybe updated to include data representative of one or more of theperformance parameters determined in step 506, including latency and/orcongestion parameters, for example.

In certain examples, a path comparison table may be maintained by device302-1 and may include one or more performance parameters for one or moreof the paths 306 connected to device 302-1. For example, FIG. 6illustrates an exemplary path comparison table 600 that may bemaintained by device 302-1. As shown in FIG. 6, path comparison table600 may include a destination address column 602, a path identificationcolumn 604, a latency parameter column 606, a cost parameter column 608,and a congestion parameter column 610. Destination address column 602may include data representative of one or more destination addressesassociated with one or more layer-2 network devices such as devices 302.In FIG. 6, destination addresses in the destination address column 602comprise MAC addresses associated with device 302-3.

Path comparison table 600 maintained by device 302-1 may includeperformance data for each provisioned path connected to device 302-1. Asillustrated, path comparison table 600 may include a row for each of thepaths 306 provisioned in system 300 and connected to device 302-1. Inthis particular example, each of the paths 306 is mapped to the samedestination address associated with device 302-3. Accordingly, the pathcolumn 604 may include data indicating each of the paths 306-1, 306-2,and 306-3 interconnection device 302-1 and device 302-3, as shown inFIG. 6.

The latency parameter column 606 and congestion parameter column 610include data representative of monitored performance metrics for paths306. The values of the latency parameters and congestion parameters maybe calculated based on monitored data in any suitable way and using anysuitable predefined parameter calculation heuristics. In certainexamples, the values of the latency parameters and the congestionparameters for paths 306 may be normalized to facilitate an unbiasedcomparison of the paths 306. For example, values of latency parametersmay be normalized to account for differences in the number of hopsspanned by each of the paths 306. As another example, values ofcongestion parameters may be normalized to account for differences inbandwidth capacities of paths 306. In the illustrated example, pathcomparison table 600 includes latency parameter values of “10,” “8,” and“9” and congestion parameter values of “5,” “4,” and “5” for paths306-1, 306-2, and 306-3, respectively. In the illustrated example, ahigher number indicates a longer latency or more congestion than thatindicated by a lower number.

In certain embodiments, a path comparison table may include otherparameters such as one or more cost parameters associated with layer-2network paths. For example, path comparison table 600 in FIG. 6 includescost parameters associated with paths 306. The cost parameter for a path306 may represent a cost to a service provider and/or network operator(e.g., a financial cost and/or a resource cost) to forward data trafficover the path. As an example, the cost to a service provider to forwarddata traffic over a path owned by the service provider may be less thancost to forward data traffic over another path owned by another serviceprovider. Cost parameter values may be defined in any suitable way,including manually by a user of system 100 through user interfacefacility 102. In the example shown in FIG. 6, path comparison table 600includes cost parameter values of “10,” “11,” and “5” for paths 306-1,306-2, and 306-3, respectively. In the illustrated example, a highercost parameter value indicates a higher cost than that indicated by alower cost parameter value.

As mentioned, a path comparison table such as path comparison table 600may be updated in step 508 of FIG. 5. In some embodiments, at leastcertain updates to the path comparison table 600 may be performeddynamically in real-time or near real-time based on monitoredperformances of one or more layer-2 network paths for which data ismaintained in the path comparison table. Accordingly, path comparisontable 600 may include up-to-date performance parameters for one or moreof the paths 306 connected to device 302-1 in FIG. 3.

Returning to FIG. 4, in certain embodiments, only the performance ofcertain selected layer-2 network paths is monitored in step 402. Forexample, the monitoring of layer-2 network paths may be restricted toonly those paths over which data traffic is being transmitted. Thus,paths over which no data traffic is being transmitted may not bemonitored. For example, device 302-1 may be configured to monitor onlythe paths 306 over which device 302-1 is forwarding data traffic. Inother examples, device 302-1 may be configured to monitor each of thepaths 306 regardless of current data traffic activity.

In step 404 of FIG. 4, an optimal one of the plurality of layer-2network paths over which data traffic is to be forwarded is selectedbased on a path selection heuristic and the monitored performance of atleast one of the plurality of layer-2 network paths. For example, one ofthe paths 306 shown in FIG. 3 may be selected as an optimal data trafficforwarding path based on a path selection heuristic and the monitoredperformance of at least one of the paths 306.

The path selection heuristic may specify one or more conditions to beused to determine an optimal layer-2 network data forwarding path from aplurality of layer-2 network paths. The path selection heuristic, whichmay be defined in any suitable way, such as by a user of system 100through user interface facility 102, may be defined as may suit aparticular implementation, data forwarding strategy, business objective,service level agreement, quality-of-service standard, etc.

In certain embodiments, the path selection heuristic may be configuredto direct utilization and comparison of data in a path comparison tablesuch as path comparison table 600. For example, parameter values forpaths 306 may be compared to identify an optimal path based on theparameter values for the paths 306, including one or more of theperformance parameters values (e.g., latency and/or congestion parametervalues) determined in step 402. The selection performed in step 404 maybe based on one or more of the parameters included in path comparisontable 600. In certain embodiments, for example, a selection of anoptimal path may be based on one or more latency parameters, congestionparameters, and cost parameters associated with paths 306.

As an example, a path selection heuristic may specify that latencyparameters be used as the sole basis for selection of an optimal path.Under this condition, in the example shown in FIG. 6, path 306-2 wouldbe selected as the optimal path over which to forward data traffic fromdevice 302-1 to device 302-3. As another example, a path selectionheuristic may specify that congestion parameters be used as the solebasis for selection of an optimal path. Under this condition, in theexample shown in FIG. 6, path 306-2 would again be selected as theoptimal path over which to forward data traffic from device 302-1 todevice 302-3. However, if a path selection heuristic specified that costparameters be used as the sole basis for selection of an optimal path,in the example shown in FIG. 6, path 306-3 would be selected as theoptimal path over which to forward data traffic from device 302-1 todevice 302-3.

A path selection heuristic may specify that a combination of one or moreof the parameters included in a path comparison table be considered todetermine an optimal data forwarding path. For example, a path selectionheuristic may specify that a sum total of parameter values (e.g.,latency, cost, and congestion parameter values) be calculated for eachpath and used to compare paths to determine which of the paths isoptimal for forwarding data traffic. Using this approach, in the exampleshown in FIG. 6, path 306-3 would be selected as the optimal path overwhich to forward data traffic from device 302-1 to device 302-3.

In certain embodiments, the path selection heuristic may specify thateach of the types of parameters included in a path comparison table begiven even weight when selecting an optimal path. In certain otherembodiments, the path selection heuristic may specify that the types ofparameters included in a path comparison table be weighted differentlywhen selecting an optimal path. For example, cost parameters may be moreheavily weighted than latency and/or congestion parameters in someimplementations.

In certain embodiments, the path selection heuristic may specify aprioritized order of paths and/or parameters to be considered whenselecting an optimal data forwarding path. For example, path 306-3 maybe a preferred path because of its relatively lower cost parametervalue. Accordingly, the path selection heuristic may specify the path306-3 be selected as long as the monitored performance of the path 306-3satisfies a certain threshold. For example, path 306-3 may be selectedas an optimal path until its congestion parameter value reaches acertain threshold, at which point, path 306-1 and/or path 306-2 may beconsidered and their parameter values compared to the parameter valuesof path 306-3 to select an optimal one of the paths 306 for forwardingdata traffic.

The above-described examples of path selection heuristics and conditionsthat may be used when selecting an optimal data forwarding path areillustrative only. Other conditions may be specified by a path selectionheuristic and considered when selecting an optimal data forwarding pathbased on the monitored performance of one or more paths.

In certain embodiments, the selection of an optimal path over which toforward data traffic may include updating a traffic forwarding table,such as a traffic forwarding table included in forwarding data 110 indata storage facility 110. For example, monitoring facility 108 ofsystem 100 may insert data representative of a selected optimal path ina traffic forwarding table. To illustrate, device 302-1 may maintain atraffic forwarding table to be used to determine where to forward datatraffic (e.g., over which of paths 306 to forward data traffic to device302-3).

Step 404 may include updating the traffic forwarding table maintained bydevice 302-1 to include data representative of a selected optimal pathover which data traffic is to be forwarded. The updating of the trafficforwarding table may configure device 302-1 to forward subsequent datatraffic over the selected optimal path. In some examples, a trafficforwarding table may be dynamically updated in real-time or nearreal-time with data representative of up-to-date selections of anoptimal data forwarding path that have been made based on monitoredperformance of one or more paths.

In certain embodiments, monitoring of a performance of at least one of aplurality of layer-2 network paths and selecting an optimal one of thepaths may be periodically repeated. This may help ensure that an optimalpath is selected based on up-to-date monitored performance data. Forexample, step 402 of FIG. 4 may be periodically repeated to repeatedlymonitor the performance of at least one of a plurality of layer-2network paths as described herein, and step 404 of FIG. 4 may beperiodically repeated to select an optimal one of the layer-2 networkpaths based on up-to-date performance parameters. The periodicallyrepeated monitoring and selecting may support dynamic updating of atraffic forwarding table as mentioned above.

In certain embodiments, monitoring of a performance of at least one of aplurality of layer-2 network paths and selecting an optimal one of thepaths may be performed in one or more background processes (e.g.,background daemons) running on a device (e.g., device 200 or one or moreof devices 302). For example, device 302-1 may be configured to performone or more steps 402 and 404 of FIG. 4 in a background process runningon the device 302-1. For instance, the monitoring of a performance of alease one of the paths 306 may be performed by one or more backgrounddaemons running on device 302-1. For example, a background daemonrunning on device 302-1 may transmit one or more ping messages over oneor more of the paths 306. Similarly, a background daemon running ondevice 302-1 may receive responses to the ping messages and utilizeddata included in the responses to determine one or more performanceparameters for one or more of the paths 306. The background daemonreceiving the responses to the ping messages may also be responsible forupdating path comparison table 600 and/or a traffic forwarding tablemaintained by device 302-1, as described above.

In step 406 in FIG. 4, data traffic is forwarded for transport over theselected one of the plurality of layer-2 network paths. For example, arequest to forward data traffic (e.g., a data packet) may be received bydevice 302-1. Device 302-1 may look to its traffic forwarding table(e.g., a lookup of the destination address) to determine over which ofthe paths 306 to forward the data traffic. The path indicated in thedata forwarding table may represent a selected optimal path, asdescribed above. The device 302-1 may forward the data packet out aningress port associated with the optimal path.

FIG. 7 illustrates another exemplary layer-2 network path performancemonitoring method 700. While FIG. 7 illustrates exemplary stepsaccording to one embodiment, other embodiments may omit, add to,reorder, and/or modify any of the steps shown in FIG. 7. In certainembodiments, system 100, device 200, and/or one or more devices 302 mayperform one or more of the steps shown in FIG. 7. In certainembodiments, one or more steps of FIG. 7 may be performed as part ofstep 402 of FIG. 4.

In step 702, a link performance is determined for at least one link(e.g., a point-to-point link) connected to a layer-2 network switchdevice. The link performance may be determined in any suitable way, suchas by transmitting a ping message and receiving a response to the pingmessage over a link connected to the layer-2 network switch device or bymonitoring performance parameters of actual data traffic transportedover each link connected to the layer-2 network switch device. In someexamples, a link may include sub-links, and step 702 may includedetermining a link performance for each sub-link and/or for thesub-links as a whole.

As an example of determining a link performance, links 304 may beprovisioned between devices 302 of system 300 as shown in FIG. 3. Eachdevice 302 may maintain an address reachability matrix specifying one ormore neighboring devices 302 that are connected to the device 302 by oneor more of the links 304. For instance, device 302-1 may maintain anaddress reachability matrix specifying addresses for devices 302-2 and302-5, which are direct point-to-point neighbors to device 302-1 andreachable from device 302-1 by way of links 304-1 and 304-5,respectively. In step 702, device 302-1 may determine a link performance(e.g., latency and/or congestion parameters) for each of the links 304-1and 304-5 connected to device 302-1.

In step 704, the link performance determined in step 702 is shared witheach neighboring layer-2 network switch device, such as by transmittingdata representative of the link performance to each neighboring layer-2network switch device over the appropriate link connected to theneighboring layer-2 switch device. For example, device 302-1 may sharethe link performances for links 304-1 and 304-5 with each of the devices302-2 and 302-5 that are direct point-to-point neighbors to device302-1. In certain embodiments, device 302-1 may also share datarepresentative of its address reachability matrix (“address reachabilitydata”) with each of the neighboring devices 302-2 and 302-5.

In step 706, link performance data is received from each neighboringlayer-2 network switch device. The link performance data may be receivedfrom each neighboring layer-2 network switch device in any suitablemanner, such as over a link connected to each neighboring layer-2network switch device. As an example, device 302-1 may receive linkperformance data from neighboring devices 302-2 and 302-5. The linkperformance data received from neighboring device 302-2 may include linkperformance data for each of the links 304-1 and 304-2 connected todevice 302-2. Similarly, the link performance data received by device302-1 from device 302-5 may include link performance data for each ofthe links 304-4 and 304-5 connected to device 302-5. In certainembodiments, device 302-1 may also receive data representative of anaddress reachability matrix from each of the neighboring devices 302-2and 302-5.

In step 708, the link performance data received from each neighboringlayer-2 network device is propagated. As an example, the linkperformance data received by device 302-1 may be propagated by device302-1 to one or more neighboring devices 302-2 and 302-5. For instance,link performance data received by device 302-1 from device 302-2 may bepropagated by device 302-1 to device 302-5. Accordingly, device 302-5may receive link performance data for links 304 connected to either ofthe device 302-1 and 302-2 (e.g., links 304-1, 304-2, and 304-5). Incertain embodiments, device 302-1 may propagate data representative ofan address reachability matrix received from each of the neighboringdevices 302-2 and 302-5.

In certain embodiments, each of the devices 302 in system 300 may beconfigured to share, receive, and propagate link performances and/orlink performance data as described above. Link performance data may bepropagated through system 100 until a convergence of link performancedata is reached and detected. Convergence of link performance data maybe detected in any suitable way. For example, each device 302 may beconfigured to determine when received link performance data containsonly link performance data that is already known to the device 302and/or contains link performance data that has been looped back to thedevice 302. In certain embodiments, devices 302 may be configured tocease propagating link performance data in response to a detectedconvergence of link performance data.

In step 710, at least one of the link performance determined in step 702and the link performance data received at step 706 is utilized todetermine a path performance (e.g., path latency and/or congestionparameters) for at least one of a plurality of layer-2 network paths. Asan example, device 302-1 may utilize one or more link performancesdetermined by device 302-1 and/or link performance data received bydevice 302-1 to determine a path performance for at least one of thepaths 306 connecting device 302-1 to device 302-3 in system 300. Thedetermination of a path performance may be performed in any suitableway. For example, where a layer-2 network path spans multiple links,link performance data for the links may be aggregated and/or otherwiseprocessed to determine a path performance for the layer-2 network path.To illustrate, device 302-1 may aggregate link performance data forlinks 304-1 in 304-2 to determine a path performance for path 306-1. Thepath performance determined in step 710 may be utilized in any of theways described above to select an optimal data forwarding path from aplurality of layer-2 network paths.

One or more of the steps 702-710 shown in FIG. 7 may be repeatedperiodically and/or for various layer-2 network switch devices. Incertain embodiments, one or more of the steps 702-710 may be configuredto be performed periodically to monitor current path performance datasuch that selections of optimal data traffic forwarding paths may bemade based on up-to-date and/or recent performance data.

In certain embodiments, one or more link performances detected in step702 and/or link performance data received in step 706 may be utilized todiscover and provision one or more layer-2 network paths. As an example,device 302-1 may utilize link performance data, as well as sharedaddress reachability data, to automatically discover and provision oneor more end-to-end layer-2 network paths between device 302-1 and one ormore other devices 302-2 through 302-5 in system 300. For instance,device 302-1 may automatically discover and provision paths 306-1,306-2, and 306-3 connecting device 302-1 and device 302-3 based on thelink performance data and/or address reachability data present at device302-1. In other embodiments, one or more layer-2 network paths may havebeen previously provisioned manually and/or using an automatic pathdiscovery protocol.

One or more of the exemplary systems and methods described herein mayprovide for improved resiliency, throughput, link utilization,satisfaction of service level agreements, quality of service, loadbalancing, reliability, efficiency, and/or scalability with respect tolayer-2 traffic forwarding functionalities, devices, and/or networks.For example, by selecting an optimal traffic forwarding layer-2 networkpath based on monitored path performance, a layer-2 network switchdevice may load balance between multiple layer-2 network pathsconnecting to a common destination device. This may be accomplished byselecting an optimal layer-2 network path, which may result in anincrease in usage of (e.g., steering traffic toward) underutilizedlayer-2 network paths and/or links and a decrease in usage of (e.g.,steering traffic away from) overly utilized layer-2 network paths and/orlinks.

In the preceding description, various exemplary embodiments have beendescribed with reference to the accompanying drawings. It will, however,be evident that various modifications and changes may be made thereto,and additional embodiments may be implemented, without departing fromthe scope of the invention as set forth in the claims that follow. Forexample, certain features of one embodiment described herein may becombined with or substituted for features of another embodimentdescribed herein. The description and drawings are accordingly to beregarded in an illustrative rather than a restrictive sense.

1. A method comprising: monitoring, by a layer-2 network switchingsystem, a performance of at least one of a plurality of layer-2 networkpaths connecting a layer-2 network switch device to another layer-2network switch device; and selecting, by the layer-2 network switchingsystem, an optimal one of the plurality of layer-2 network paths overwhich to forward data traffic based on a path selection heuristic andthe monitored performance of the at least one of the plurality oflayer-2 network paths.
 2. The method of claim 1, further comprisingforwarding, by the layer-2 network switching system, the data trafficout an ingress port of the layer-2 network switch device for transportto the another layer-2 network switch device over the selected one ofthe plurality of layer-2 network paths.
 3. The method of claim 1,wherein the monitoring comprises: transmitting, by the layer-2 networkswitching system, a ping message from the layer-2 network switch deviceto the another layer-2 network switch device over the at least one ofthe plurality of layer-2 network paths; receiving, by the layer-2network switching system, a response to the ping message from theanother layer-2 network switch device over the at least one of theplurality of layer-2 network paths; and determining the performance ofthe at least one of the plurality of layer-2 network paths based on theresponse.
 4. The method of claim 3, wherein the determining theperformance of the at least one of the plurality of layer-2 networkpaths comprises determining a latency parameter for the at least one ofthe plurality of layer-2 network paths.
 5. The method of claim 3,wherein the determining the performance of the at least one of theplurality of layer-2 network paths comprises determining a congestionparameter for the at least one of the plurality of layer-2 networkpaths.
 6. The method of claim 5, wherein: the ping message comprises achain of data packets spaced apart by a transmission time interval; andthe determining of the congestion parameter includes detecting adeviation from the transmission time interval in the response to theping message and calculating the congestion parameter based at least inpart on the detected deviation.
 7. The method of claim 1, furthercomprising: maintaining, by the layer-2 network switching system, datarepresentative of a traffic forwarding table; wherein the selecting ofthe optimal one of the plurality of layer-2 network paths over which toforward the data traffic comprises inserting data representative of theoptimal one of the plurality of layer-2 network paths in the trafficforwarding table; and forwarding, by the layer-2 network switchingsystem, the data traffic to the optimal one of the plurality of layer-2network paths based on the data representative of the optimal one of theplurality of layer-2 network paths included in the traffic forwardingtable.
 8. The method of claim 1, further comprising: maintaining, by thelayer-2 network switching system, data representative of a trafficforwarding table; periodically repeating, by the layer-2 networkswitching system, the monitoring of the performance of the at least oneof the plurality of layer-2 network paths connecting the layer-2 networkswitch device to the another layer-2 network switch device; anddynamically updating, by the layer-2 network switching system, thetraffic forwarding table based on the monitored performance of the atleast one of the plurality of layer-2 network paths.
 9. The method ofclaim 1, further comprising maintaining, by the layer-2 networkswitching system, data representative of a path comparison table, thepath comparison table including at least one performance parameterrepresentative of the monitored performance of the at least one of theplurality of layer-2 network paths, wherein the at least one performanceparameter comprises a latency parameter and a congestion parameter forthe at least one of the plurality of layer-2 network paths.
 10. Themethod of claim 9, wherein the path comparison table further comprises acost parameter for the at least one of the plurality of layer-2 networkpaths.
 11. The method of claim 10, wherein the selecting of the optimalone of the plurality of layer-2 network paths over which to forward thedata traffic is based on at least one of the latency parameter, thecongestion parameter, and the cost parameter for the at least one of theplurality of layer-2 network paths.
 12. The method of claim 1, wherein:the layer-2 network switch device comprises an Ethernet switch devicewithin an optical transport network; and the monitoring and theselecting are performed within a background process running on theEthernet switch device.
 13. The method of claim 1, wherein themonitoring comprises: determining, by the layer-2 network switchingsystem, a link performance for at least one link connected to thelayer-2 network device; sharing, by the layer-2 network switchingsystem, the link performance with each layer-2 network deviceneighboring the layer-2 network device; receiving, by the layer-2network switching system, link performance data from the each layer-2network device neighboring the layer-2 network device; propagating, bythe layer-2 network switching system, the link performance data receivedfrom the each layer-2 network device neighboring the layer-2 networkdevice; and utilizing, by the layer-2 network switching system, at leastone of the link performance for the at least link connected to thelayer-2 network device and the received link performance data todetermine the performance of the at least one of the plurality oflayer-2 network paths.
 14. The method of claim 13, further comprisingutilizing, by the layer-2 network switching system, the link performancedata and shared address reachability data to automatically discover andprovision the plurality of layer-2 network paths.
 15. The method ofclaim 1, tangibly embodied as computer-executable instructions on atleast one computer-readable medium.
 16. A system comprising: amonitoring facility configured to monitor a performance of at least oneof a plurality of layer-2 network paths connecting a layer-2 networkswitch device to another layer-2 network switch device, and select anoptimal one of the plurality of layer-2 network paths over which toforward data traffic based on a path selection heuristic and themonitored performance of the at least one of the plurality of layer-2network paths; and a forwarding facility configured to forward the datatraffic to the selected one of the plurality of layer-2 network pathsfor transport from the layer-2 switch device to the another layer-2switch device.
 17. The system of claim 16, wherein the monitoringfacility is configured to monitor the performance of the at least one ofthe plurality of layer-2 network paths by transmitting a ping messagefrom the layer-2 network switch device to the another layer-2 networkswitch device over each of the layer-2 network paths, receiving aresponse to the ping message from the another layer-2 network switchdevice over each of the layer-2 network paths, and determining theperformance of each of the layer-2 network paths based on the response.18. The system of claim 16, wherein: the forwarding facility isconfigured to maintain a traffic forwarding table; and the monitoringfacility is configured to repeatedly monitor the performance of the atleast one of the plurality of layer-2 network paths connecting thelayer-2 network switch device to the another layer-2 network switchdevice, and dynamically update the traffic forwarding table based on themonitored performance of the at least one of the plurality of layer-2network paths.
 19. The system of claim 16, wherein the monitoringfacility is configured to select the optimal one of the plurality oflayer-2 network paths over which to forward the data traffic based on atleast one of a latency parameter, a congestion parameter, and a costparameter associated with the at least one of the plurality of layer-2network paths.
 20. The system of claim 16, wherein the monitoringfacility is configured to monitor the performance of the at least one ofthe plurality of layer-2 network paths by determining a link performanceat least one link connected to the layer-2 network device, sharing thelink performance with each layer-2 network device neighboring thelayer-2 network device, receiving link performance data from the eachlayer-2 network device neighboring the layer-2 network device,propagating the link performance data received from the each layer-2network device neighboring the layer-2 network device, and utilizing atleast one of the link performance for the at least link connected to thelayer-2 network device and the received link performance data todetermine the performance of the at least one of the plurality oflayer-2 network paths.
 21. A system comprising: a first layer-2 networkswitch device; and a second layer-2 network switch device connected tothe first layer-2 network switch device by a plurality of layer-2network paths; wherein the first layer-2 network switch device isconfigured to monitor a performance of each of the layer-2 networkpaths, select an optimal one of the layer-2 network paths through whichto forward data traffic to the second layer-2 network switch devicebased on a path selection heuristic and the monitored performance ofeach of the layer-2 network paths, and forward the data traffic to thesecond layer-2 network switch device over the selected optimal one ofthe layer-2 network paths.
 22. The system of claim 21, wherein the firstlayer-2 network switch device and the second layer-2 network switchdevice each comprises at least one of an Ethernet switch device and aMedia Access Control (“MAC”) addressing device within an opticaltransport network.